Illumination-quality indicator



Sept. 30, 1958 D. w. NoRwooD 2,854,193

ILLUMINATIoN-QUALITY INDICATOR Filed May 3l, 1955 2 Sheets-Sheet 1DONALD NORWOOD BY QMW Mm ATTOQNDS Sept. 30, 1958 D. w, NoRwooDILLUMINATIoN-QUAL'ITY INDICATOR 2 Sheets-Sheet 2 Filed May 3l, 1955 m .Wmm W N WW mw. A M 0 -ance of a subject is of primary importance.

United States Patent O lLLUMINATION-QUALTY INDICATOR Donald W. Norwood,Pasadena, Calif.

Application May 31, 1955, Serial No. 512,219

7 Claims. (Cl. 23S-64.7)

'This invention relates to devices for providing an indication of theillumination quality of light on an object which is to be reproduced inthe form of a picture.

In the fields of photography and television the appear- This appearanceis usually atfectedto a considerable extent by the intensity and thedirectional arrangement of each of the various elements of illuminationacting on the subject. It is generally considered good practice to haveone dominant element of illumination. This is known as the keylight.There is usually at least one element of secondary illumination. This isknown as the fill-light. The sources of the key-light and the fill-lightare spacially separated with respect to each other and to the subject,so that the key-light illuminates some surfaces of the camera-side ofthe three-dimensional subject, and the fill-light illuminates othersurfaces of the camera-side of the subject.

The quality of a picture of either the photographic or electronic typedepends to a considerable extent on the relationship of the intensitiesof the key-light and the filllight. A comparison of these two valuesestablishes a ratio. This ratio is sometimes calledillumination-contrast or illumination-contrast-ratio. In practice theoperator may encounter a ratio which is too low. In such a case themodeling effect, which enhances the illusion of a three-dimensionalsubject on a two-dimensional picture surface, is diminished or lost. Onthe other hand, at times the ratio may be too high. In this casedifficulty is encountered with the limitations of the recording medium.The end result in this case is a decrease or total loss of tone valuesin either the fill-light illuminated areas or in the key-lightilluminated areas of the subject, or in both.

Each recording medium, such as (1) Black-and-white film pictures (a)Transparency prints (b) Paper prints (2) Color lm pictures (a)Transparency prints (b) Paper prints (3) Black-and-white televisionpictures (4) Color television pictures operates to best advantage underconditions of an illumination-contrast-ratio which is peculiarly suitedto that medium. In each case the acceptable ratio is not limited to onevalue but rather extends over a band of values. On each side of theoptimum value band there is a gradual or rapid decrease inacceptability.

The total range of ratio values that should be considered extends from aratio of 1/ 1 up to a ratio of 16/1.

Although some recording mediums offer some small degree of flexibilityin adaption to variations in illumination-contrast, others presentpractically none. This is particularly true in the case of lms which aremachine developed by the time-and-temperature method. In all caseshowever, the best picture quality results are achieved Mice if theillumination-contrast is adjusted to meet the requirements of therecording medium, rather than trying to proceed by a converse method.

It is difficult for the operator of a camera to arrange the illuminationof an object so as to obtain a picture of the best possible quality.vThis is particularly true if a series of pictures is to be taken, withall of the pictures to be of substantially the same quality. Also,amateur camera operators iind it difficult to select proper illuminationto provide pictures of uniform high quality. This diiiiculty isincreased if the camera operator uses more than one type film, such asblack-and-white film and color film, because the optimum illuminationcontrast relationship is different for films of different types.

These difliculties are overcome in the present invention by the use or"a device which provides an indication of the illumination quality forvarious light intensities with respect to the characterstics of a givenrecording medium. The device is provided with a scale representingkey-light intensities and another scale representing fill-lightintensities. One of the scales is movable with respect to the other, andone of the scales carries a numerical indicator for showing theillumination-contrast-ratio. One of the scales also carries a graphicalindicator for showing the picture quality obtainable with at least onetype of recording medium for the various settings of the two scales withrespect to one another.

This device makes quality control of pictures easy to achieve by bothprofessional and amateur camera operators. The essential information ispresented both in numerical and in graphical form, so that the deviceprovides a precise indication of the illumination-contrast-ratio, and italso provides an indication of the picture quality obtainable with anyparticular illumination-contrast-ratio. The numerical indication of theillumination-contrastrato may be employed in selecting properillumination for any type of recording medium. The graphical indicationof picture quality is limited to a particular type of recording medium,but a plurality of graphical indicators may be employed so as to coverseveral different types of recording mediums.

The invention is explained in detail with reference to the drawings, inwhich:

Fig. 1 illustrates the illumination of a subject by keylight andfill-light;

Fig. 2 is a chart showing the picture quality obtainable with respect tothe illumination-contrast-ratio for two types of recording mediums;

Fig. 3 illustrates how the device of the present invention may bemounted on the back of a light meter;

Fig. 4 is an enlarged plan View `of the quality control device of thepresent invention;

Fig. 5 is a side view of the device of Fig. 4;

Fig. 6 is a sectional view along line 6 6 of Fig. 4, and

Fig. 7 is a plan view of the rotatable member of Fig. 4.

Fig. 1 illustrates a subject which is illuminated by keylight which is.produced by a source which is disposed about with respect to the axisalong which the subject is observed. The other side of the subject isilluminated by fill-light which should have a certain intensity withrespect to that of the key-light in order to obtain a picture of thebest possible quality with a particular type recording medium.

For ordinary recording mediums, the illuminationcontrast-ratios whichshould be considered extend from 1/ 1 to 16/1. Somewhere within thisrange will be found the band of optimum contrast ratios for therecording medium which is to be employed.

The picture quality with respect to illumination-contrast-ratio which isobtainable with a certain recording medium may be indicated in graphform. Fig. 2 is a chart having rectangular coordinates which indicatesthe picture quality obtainable on transparency prints from aconventional black-and-white and from a conventional color film forillumination-contrast-ratios between l/ l and 16/1. In the case of eachrecording medium, it will be found that the curve starts at a qualitylevel somewhat below maximum for an illumination-contrastratio of l/l,that the curve rises to a maximum value band as theillumination-contrast-ratio increases, and then the curve decreases to alow value as the illuminationcontrast-ratio approaches 16/1. The picturequality axis may be divided into levels designating the type of pictureobtainable. These levels are designated Good, Fair, and Poor on thechart of Fig. 2.

In order to use the quality control device of the present invention, theintensity of the effective key-light and the intensity of the effectivefill-light should be ascertained.

This may be accomplished by using a suitable light meter.

Preferably, the quality control device of the present invention ismounted on the light meter which is employed to measure the key-lightand fill-light intensities. Fig. 3 illustrates such an arrangementwherein a light meter 16 has the quality control device l?. mounted onthe back side of the light meter. The light meter is provided with amovable hood 14 for changing the range of the light meter.

The quality control device is supported on a backing member 16 having aninner face lf3 which abuts against the back of the light meter. Fouropenings 19 are provided in the backing member for accommodating screwsfor joining the quality control device to the light meter. The backingmember has a shape which mates with the contour of the light meter sothat it appears to be an integral part of the housing for the lightmeter.

The backing member is provided with a cylindricalshaped protrusion 20which is centrally located on the backing member. A recessed areaextends around the protrusion. A disk-shaped member 22 serves as therotatable member of the device. The rotatable member is provided with acentrally-located portion 24 of cylindrical shape which is offsetoutwardly from the remaining peripheral portion 26 of the member. Theoffset portion 24 has inner surfaces which mate with the protrusion 20on the backing member to permit rotation of the diskshaped member aboutthe protrusion on the backing member. The outer periphery of therotatable member is provided with a knurled edge 27 so that the membermay be rotated with ease by the operator. A portion of the backingmember is cut away at each side so as to provide access to the knurlededge of the rotatable member.

A friction element 2S is located in a recess in the backing member, andit rubs against the back of the rotatable member to provide sufcientfriction to prevent movement of the rotatable member except when theoperator rotates it with his thumb or finger. The friction element maybe a felt pad or a strip of spring metal bent to a desired shape.

A stop pin 30 is ahxed to the backing, and it extends through an arcuateslot 32 in the rotatable member. The stop pin 30 and the slot 32 serveto limit the rotation of the rotatable disk to suitable limits, say toan arc of about 90.

A face plate 34 is secured to the backing member by a plurality ofscrews 36. The face plate secures the rotatable member between the faceplate and the backing member.

A key-light scale 38 is located on the rotatable member, and afill-light scale 40 is located on the face plate. These two scales havedelineations representing light intensities, say intensities from 1 to128 foot-candles or multiples of these values, for the key-light scaleand intensities from .30 to 128 foot-candles or multiples of thesevalues for the till-light scale. Preferably these two scales areexponential types.

A numerical scale 42 is located along a portion of the outer peripheryof the rotatable member, and this scale serves to provide numerators forthe indicator fraction which designates the illumination-contrast-ratio.Such an arrangement indicates the ratio of the intensity of thekey-light to the intensity of the fill-light. lt will be apparent thatthe ratio of the fill-light intensity to that of the key-light could bedisplayed if desired.

A pair of indicator lines or graphs 44 and 46 are provided on anotherportion of the outer periphery of the rotatable member. These two graphsrepresent the picture quality obtainable with respect to theilluminationcontrast-ratio for two types of recording mediums, say forcolor film and for black-and-white film. The graphs 44 and 46 correspondto the curves for color film and for blacl'-andwhite film which areillustrated in Fig. 2. The graphs 44 and 46 are derived by translatingthe rectangular coordinate curves of Fig. 2 to polar coordinates so thatthey may be employed on the rotatable member of the quality controldevice.

A pair of apertures 4S and Sti are provided in the face plate forexposing portions of each of the graphs. A pair of quality scales 52 and54 are located on the face plate adjacent the apertures for providingdesignations of picture quality along the graphs for the varioussettings of the key-light scale. ln the arrangement shown in Fig. 4these scales are provided with the designations Good, Fair, and Poor, sothat the operator can tell at a glance the quality of the pictureobtainable for the light intensities in question.

lt will be apparent that the graphical information which is provided bythe indicator lines 44 and 46 may be provided in other manners. By wayof example, the information may be represented by colored areas ratherthan by discrete lines.

The face plate is also provided with an aperture 56 which serves toexpose at least one of the numbers ou the illumination-contrast scale42. The face plate is provided with the denominator 58 for theilluminationcontrast-ratio. As shown in Fig. 4, the denominator is thenumeral l and it is located directly below the aperture S6 through whichthe numerators may be observed.

Preferably, the backing member 18 is composed of a plastic so that itmay be fabricated with ease. However, it may be composed of othermaterials if desired. The rotatable member 22 and the face plate 34 maybe made of sheet metal or sheet plastic. The scales and graphs may beengraved directly in the material and then filled with a suitable paint,or they may be printed on the various members or applied to them bymeans of decalcomanias.

The rotatable disk 22 may be turned so that any selected value on thekey-light scale may be brought adjacent to any selected value on thefill-light scale, within signicant limits. For each setting of thekey-light scale, the illumination-contrast-ratio will be displayed atthe aperture 56. For each illumination-contrast-ratio, there will be arelated designation of picture quality obtainable with color film orwith black-and-white film, and these designations may be observed at theapertures 48 and 50.

As an example, assume a value of 64 for the intensity of the key-lightand a value of 8 for the intensity of the fill-light. The rotatablemember is turned until 64 on the key-light scale is adjacent 8 on thefill-light scale. The numerical value of the illumination-contrast-ratiowill be 8/1, and this can be observed at the aperture 56. The quality ofthe picture obtainable will be in the Fair-to-Poor region on the scaleS2 for color film and in the Medium-Fair region on the scale 54 forblack-and-white film.

ln operation, the camera man rst makes a measurement of the intensity ofthe effective key-light and the intensity of the effective fill-light.This may be accomplished by the use of a foot-candle meter havingsuitable acceptance angle, say a solid angle of about 21r steradians.The foot-candle meter is ordinarily `used at the position of thesubject. The operator then turns the rotatable member 22 with his thumbuntil the measured key-light intensity is located opposite the ll-lightintensity which he has measured.

The operator then observes through the aperture 48 or through theaperture 50, depending upon the type of film which he is using, theposition of the indicator line or graph with respect to the associatedquality scale. In this maner he can tell at a glance the quality ofpicture which can be obtained with the particular illuminationconditions then existing.

Thus, the indicator device evaluates the quality of the illuminationwith respect to a given recording medium in addition to predicting thequality of the picture which will result. For a given recording mediumthe illumination quality and the resulting picture quality aresubstantially parallel. The graphical indicator on the device evaluatesboth of these factors.

The operator may also observe the illumination-contrast-ratio at aglance. The illumination-contrast-ratio is primarily useful when theoperator is employing a recording medium other than that for which thegraphical indicators are designed.

An alternative way for using the quality control device is to firstadjust the rotatable disk 22 until the desiredillumination-contrast-ratio is shown at the aperture 56, or until thequality indicator shows the desired quality value on one of the qualityscales. The camera man then measures the intensity of the key-light.Then he notes the location of the key-light intensity value on thekeylight scale, and the intensity of the lill-light required to producethe desired illumination can be read from the till-light scale at thislocation. The camera operator then adjusts the till-light intensityuntil the indicated value is obtained.

Although the device of the present invention has been described withreference to providing designations of picture quality for color filmand for black-and-white film, it will be apparent that the device may bearranged to designate picture quality for substantially any type ofrecording medium. Graphs for other types of recording mediums may beprepared by first providing charts in the form of rectangularcoordinates, as illustrated in Fig. 2, and then converting therectangular coordinates to polar coordinates so as to provide graphswhich may be employed on the rotatable member of the device.

Although the quality control device may be aixed to a light meter, itwill be apparent that the device is equally useful as a separate unit,and it is not necessary to attach it to a light meter.

I claim:

1. An illumination-quality indicator device comprising a key-light scalehaving delineations on it indicating a series of light intensities, a:till-light scale located adjacent the key-light scale and havingdelineations on it indicating a series of light intensities, means forproviding relative movement between the two scales, the spacing of saidlight intensities being the same on both of said scales and beingexponential so that for each relative setting of the scales the keylight intensities are in a predetermined ratio to the fill-lightintensities with that ratio being uniform along the length of thescales, means for providing a numerical indication of the ratio of theintensities of the key-light and the fill-light for various settings ofthe two scales with respect to one another, and graphical indicatormeans responsive to relative movement between the two scales forproviding an indication of the picture quality obtainable for aplurality of recording mediums at various settings of the two scaleswith respect to one another.

2. An illumination-quality indicator device for mounting on the back ofa light meter comprising a backing member having a shape which mateswith the shape of vthe light meter on which it is to be mounted, theback- '6 ing member having a recessed area centrally located ou itsouter face, a rotatable disk-shaped member having inner surfaces whichmate with the recessed area of the backing member to permit rotation ofthe disk-shaped member on the backing member, delineations located alongan inner portion of the rotatable member providing a first circularscale representing light intensities, a numerical scale located alonganother portion of the rotatable member for providing a numericalrepresentation of illumination contrast, at least one graphical meanslocated along an outer portion of the rotatable member representing thepicture quality with respect to the illumination-contrast-ratioobtainable with at least one type of recording medium, a face platehaving a circular aperture in it which mates with the portion of therotatable member on which the first circular scale is located,delineations located on the face plate adjacent the circular apertureproviding a second circular scale representing light intensities, andscale means located on the face plate and disposed adjacent thegraphical means on the rotatable member providing designations ofpicture quality along the graphical means for'the various settings ofthe first scale with respect to the second scale, one of said first andsecond circular scales representing a series of key-light intensitiesand the other representing a series of till-light intensities, thespacing of said light intensities being the same on both of said firstand second scales and being exponential so that for each relativesetting of the scales the key-light intensities are in a predeterminedratio to the till-light intensities with that ratio being uniform alongthe length of the scales.

3. An illumination-quality indicator device for mounting on the back ofa light meter comprising a backing member having an inner face of ashape which mates with the shape of the light meter on which it is to bemounted, the backing member having a cylindricalshaped protrusioncentrally located on its outer face, a rotatable disk-shaped memberhaving a centrally-located portion of cylindrical shape which is offsetfrom the remainder of the member, with the offset portion having innersurfaces which mate with the protrusion on the backing member to permitrotation of the disk-shaped member around the protrusion on the backingmember, delineations located along the periphery of the offset portionof the rotatable member providing an exponential scale representingkey-light intensities, a numerical scale located along a portion of theouter periphery of the rotatable member for providing a numericalrepresentation of illumination contrast, a pair of graphs located alonganother portion of the outer periphery of the rotatable memberrepresenting the picture quality obtainable with respect to theillumination-contrast-ratio for two types of recording mediums, a faceplate having a circular aperture in it which mates with the outerperiphery of the ofset portion of the rotatable member, delineationslocated on the face plate adjacent the circular aperture providing anexponential scale representing filllight intensities, the face platehaving an aperture in it for exposing a portion of the numerical scalerepresenting illumination contrast, the -face plate also having a pairof apertures in it for exposing portions of each of the graphs, scalemeans located adjacent the pair of apertures providing designations ofpicture quality along the graphs for the various settings of the scalesrepresenting light intensities, and means for securing the face plate tothe backing member with the face plate securing the rotatable memberbetween the face plate and the backing member, said two exponentialscales representing key-light and fill-light intensities having thelight intensities thereon spaced the same on one scale as on the otherso that for each relative setting of these Scales the key-lightintensities are in a predetermined ratio to the fill-light intensitieswith that ratio being uniform along the length of the scales.

4. An illumination-quality indicator comprising a lirst member having arst scale formed thereon dening a series of key-light intensities, asecond member having a second scale formed thereon adjacent saidkey-light scale and defining a Series of ll-light intensities, meansconnecting said members together for relative adjusting movement to varythe setting of one scale relative to the other, the spacing of saidlight intensities being the same on both of said scales and beingexponential so that for each relative setting of the scales thekey-light intensities are in a predetermined ratio to the fill-lightintensities with that ratio being uniform along the length of thescales, and means on said two members relatively movable with themembers and acting to indicate the illumination quality for variousrelative settings of the key-light and fill-light scales.

5. An illumination-quality indicator as recited in claim 4 in which saidlast mentioned means comprise markings 0n said members in addition tosaid scales forming a numerical indication of the illumination contrastratio.

6. An illumination-quality indicator as recited in claim 4 in which saidlast mentioned means comprise a graphical indicator for indicating thepicture quality obtainable for at least one type of recording medium.

7. An illumination-quality indicator comprising a first circular scalehaving delineations on it indicating a series of key-light intensities,a second circular scale located adjacent and disposed concentricallywith respect to thev rst scale and having delineations on it indicatinga series of fill-light intensities, means for rotating one of' thescales with respect to the other, the spacing of said light intensitiesbeing the same on both of said scales and being exponential so that foreach relative setting of the scales the key-light intensities are in apredetermined ratio to the ll-light intensities with that ratio beinguniform along the length of the scales, a graph aixed to the first scaleand providing a representation in polar coordinates of the picturequality with respect to the illumination-contrast-ratio which isobtainable with a recording medium of a predetermined type, and a thirdscale affixed to the second scale for providing designations of picturequality along the graph for various set tings of the two first mentionedscales with respect to one another.

References Cited in the ile of this patent UNITED STATES PATENTS1,429,463 Squyer Sept. 19, 1922 2,152,604 Perry Mar. 28, 1939 FOREIGNPATENTS 753,426 France Aug. 7, 1933

